The conformations and stabilities of loop structures and adjacent stem regions will be studied in series of oligodeoxyribonucleotides prepared chemically by "block" condensation methods and isolated in a state of high chemical purity. The results are expected to aid in the understanding of the shape and properties of DNA cruciform structures and the structural elements in the genomes of single-stranded DNA viruses. The methods to be used consist of differential molar absorptivity analysis, measurement of molar absorptivity - temperature profiles, NMR, circular dichroism, calorimetry, and X-ray crystallography.